Active Directory continues to be one of the most widely deployed identity platforms, even as organizations accelerate cloud adoption and integrate with Entra ID. Because AD underpins authentication, DNS, GPO, and hybrid identity, it must be designed and maintained according to modern best practices. This guide brings together Microsoft aligned recommendations and real-world enterprise standards for building a secure, scalable, and reliable AD environment in 2025.

Domain Naming Best Practices

Selecting the AD DNS name is a long-term architectural choice that affects certificates, hybrid identity, and future migrations.

• Avoid .local and other non-routable namespaces
• Use a domain you own such as contoso.com or corp.contoso.com
• Using the same internal and external domain is supported with split-brain DNS
• Many enterprises prefer an internal subdomain (ad.domain.com) for clarity
• Use only letters, numbers, and hyphens
• Avoid underscores because they violate DNS naming standards
• Routable namespaces simplify TLS certificates, UPN mapping, hybrid identity, and Entra ID Connect Sync

Domain Controller Naming Standards

Domain controllers should follow a predictable, descriptive naming pattern.

• Use a consistent format such as DC01, DC02, DC-CHI01
• Keep names under 15 characters for NetBIOS compatibility
• Use only alphanumeric characters and hyphens
• Avoid special characters that complicate SPNs and DNS registration

OU Design and Structure

A clean OU structure improves manageability, GPO targeting, and delegation.

• Do not use the default Users or Computers OU containers
• Create dedicated OUs such as:
  • Workstations
  • Servers
  • Service Accounts
  • Admin Workstations
• Use a functional OU structure rather than department-based
• Avoid deep nesting
• Apply most GPOs at logical, high-level OUs for consistency

Domain Controller Business Continuity

Domain controllers must be continuously available for AD to function.

• Perform regular System State backups on all DCs
• Periodically test backup restores
• Run supported OS versions like Windows Server 2019, 2022, or 2025
• Do not shut down DCs during normal operation, even in Test environments
• Test environments can use one DC, but production requires at least two for redundancy
• Remote sites that must authenticate offline may need a local DC

DNS Configuration Best Practices

DNS is the foundation of AD. Misconfigured DNS causes replication failures, slow logons, and GPO issues.

• Single DC: point primary DNS to itself
• Two DCs: each DC should use the other DC as primary and itself second
• Larger environments should follow the same pattern
• Do not use public DNS servers on NIC settings
• Configure forwarders on the DNS server instead
• Use the server’s real IP, not 127.0.0.1
• Ensure AD-integrated DNS zones replicate to all DCs

Administrative Tiering Model (Tier 0, Tier 1, Tier 2)

Microsoft strongly recommends a tiered administration model to prevent credential theft.

• Tier 0 includes DCs, PKI, and privileged accounts
• Tier 1 includes servers and application hosts
• Tier 2 includes workstations and user endpoints
• Admins must not cross tiers
• Tier 0 admins may only sign in to Tier 0 systems
• This blocks lateral movement paths like Pass-the-Hash

Privileged Access Workstations (PAWs)

PAWs are the safest way to perform privileged administration.

• Used exclusively for privileged actions
• Hardened with restricted software
• Limited internet access
• No email or web browsing
• Strongly recommended for Domain Admins and Tier 0 roles

Domain Administrator Account Best Practices

Privileged accounts require strict protection.

• Every admin must have separate daily-use and elevated accounts
• Example: John.Smith and John.Smith-Admin
• Use strong, unique passwords for admin accounts
• Never reuse or share admin credentials
• Monitor privileged activity through SIEM or MDR
• Enforce MFA for all privileged access paths

Service Account Best Practices

Service accounts are common attack vectors and must be managed properly.

• Use Group Managed Service Accounts (gMSA) whenever possible
• Rotate passwords for non-gMSA accounts
• Assign least privilege
• Avoid giving any service account Domain Admin rights
• Document all services tied to each account

Time Synchronization Best Practices

Kerberos requires accurate time. AD environments must follow the proper time hierarchy.

• The forest root PDC Emulator should sync with external NTP
• Other DCs should follow AD’s internal time hierarchy
• Single DC environments sync externally
• Multi-site environments may use local external NTP if WAN conditions require it

Useful commands include w32tm configuration, resync, and verification.

Group Policy Best Practices

GPOs should standardize workstation and server configuration while minimizing complexity.

Recommended categories include:

• Mapping network shares
• Deploying printers
• Enforcing password and lockout policies
• Configuring Windows Firewall
• Managing browser settings
• Disabling insecure protocols
• Creating shortcuts
• Applying Windows 10 and 11 security baselines

Security Hardening Best Practices

Reducing the AD attack surface is essential.

• No standard user accounts in Domain Admins
• Disable LLMNR and NetBIOS where possible
• Disable SMBv1 everywhere
• Apply least privilege for NTFS and share permissions
• Send DC logs to a central SIEM
• Monitor privileged groups for membership changes
• Disable older TLS versions
• Reduce or eliminate NTLM usage where possible
• Disable WDigest credential caching

PKI and Certificate Services Best Practices

Certificates support LDAPS, device authentication, and many security features.

• Use an offline root CA and online issuing CA
• Use secure templates with minimal permissions
• Use shorter certificate lifetimes where appropriate
• Log and audit certificate enrollment
• Keep CAs updated and secured like Tier 0 assets

Replication and Site Topology Best Practices

Healthy replication ensures consistent AD data everywhere.

• Create AD Sites that match real network topology
• Assign subnets properly so clients authenticate locally
• Use Site Link costs that reflect actual WAN performance
• Monitor replication health regularly using Repadmin
• Avoid unnecessary hub-and-spoke or fully meshed topologies

Schema and Extension Management

Schema changes are permanent and must be controlled.

• Extend the schema only during planned windows
• Backup the schema master before extending
• Document all schema changes
• Avoid third-party tools requiring undocumented schema updates

Hybrid Identity Best Practices (Entra ID)

For organizations syncing with Entra ID or Microsoft 365:

• Use modern Azure AD Connect versions or Entra Cloud Sync
• Do not sync privileged AD groups into Entra ID
• Use verified domains in UPN suffixes
• Enable Entra ID Protection and Conditional Access
• Choose Password Hash Sync or PTA based on business needs
• Monitor Azure AD Connect health alerts

Backup and Recovery Strategy

Reliable recoverability is critical for AD resilience.

• Perform full backups plus System State
• Use offline or immutable storage for protection
• Maintain documented AD recovery playbooks
• Test full DR scenarios at least annually

Domain Controller Health Validation

Validate DC health after deployments, migrations, patches, or role changes.

Useful commands include:

• DCDiag
• DCDiag /Test:DNS
• Repadmin /Showreps
• Repadmin /Replsum
• Repadmin /Syncall
• Netdom query fsmo
• Netdom query dc

Saving the output provides a verified baseline for audits and future troubleshooting.

Conclusion

Active Directory is still a mission-critical identity infrastructure. Following modern best practices for domain naming, OU structure, DNS configuration, privileged access, time synchronization, hardening, and monitoring ensures your AD environment remains secure, stable, and future-ready. These recommendations reflect real-world enterprise standards and Microsoft aligned guidance for 2025 and beyond.